Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $182.67   8.477%   $198.1549   $198.15   $198.15   $198.20  
  Purchase #2 $246.52   10.855%   $273.2797   $273.28   $273.30   $273.30  
  Purchase #3 $228.94   6.859%   $244.643   $244.64   $244.65   $244.60  
  Purchase #4 $8.42   9.378%   $9.2096   $9.21   $9.20   $9.20  
  Purchase #5 $208.95   9.687%   $229.191   $229.19   $229.20   $229.20  
  Purchase #6 $247.84   10.358%   $273.5113   $273.51   $273.50   $273.50  
  Purchase #7 $238.61   10.564%   $263.8168   $263.82   $263.80   $263.80  
  7 purchase totals = $1,361.95       $1,491.8063   $1,491.80   $1,491.80   $1,491.80